A variety of parallel optical communications modules exist for simultaneously transmitting and/or receiving multiple optical data signals over multiple respective optical data channels. Parallel optical transmitter modules have multiple optical transmit channels for simultaneously transmitting multiple optical data signals over multiple respective optical waveguides (e.g., optical fibers). Parallel optical receiver modules have multiple optical receive channels for simultaneously receiving multiple respective optical data signals over multiple respective optical waveguides. Parallel optical transceiver modules have multiple optical transmit channels and multiple optical receive channels for simultaneously transmitting and receiving multiple optical data signals over multiple respective transmit and receive optical waveguides. Bidirectional (BiDi) parallel optical transceiver modules have multiple BiDi channels for simultaneously transmitting and receiving optical data signals over each channel.
A typical layout for a parallel optical communications module includes a module housing, a module circuit board, such as a printed circuit board (PCB), disposed inside of the housing, and various electrical and optoelectronic components (i.e., laser diodes and/or photodiodes) mounted on the module circuit board. Such mounting arrangements are often referred to as mid-plane or chip-on-board (COB) mounting arrangements. In a typical COB mounting arrangement, a plurality of laser diodes, a plurality of photodiodes, a laser diode driver integrated circuit (IC), a receiver IC, and various other electrical components are mounted on and electrically interconnected with the module circuit board.
Parallel optical communications modules that use COB mounting arrangements are often configured to plug into and electrically interconnect with sockets mounted on a system PCB, such as a land grid array (LGA) socket, for example. An LGA socket has arrays of electrical contacts commonly disposed on its upper and lower surfaces. For example, the array of electrical contacts disposed on the lower surface may be a ball grid array (BGA) and the array of electrical contacts disposed on the upper surface may be an LGA. The electrical contacts disposed on the upper surface of the LGA socket are typically soldered to respective electrical contacts of an array of electrical contacts disposed on a lower surface of the module PCB to electrically interconnect the module PCB and the LGA socket. The electrical contacts disposed on the lower surface of the LGA socket are electrically interconnected with respective electrical contacts of an array of electrical contacts disposed on the upper surface of the system PCB. In order to maintain a good electrical connection between the electrical contacts disposed on the upper surface of the LGA socket and the electrical contacts disposed on the lower surface of the module, a proper force needs to be maintained on the module to press it against the LGA socket.
Laser diodes are very sensitive to temperature. Generally, in order to increase the speed of laser diodes without sacrificing reliability, the operating temperatures of the laser diodes need to be maintained at or below some maximum allowable temperature. Heat dissipation solutions for optical communications modules are designed to prevent the temperatures of the laser diodes from rising above impermissible levels. The laser diodes and photodiodes are often arranged in respective arrays formed in respective semiconductor chips. These chips and the laser diode driver and receiver IC chips are often mounted on one or more metal heat sinks of the module circuit board. Heat generated by the chips is dissipated into the heat sink. Air flow through the housing is often used to provide convective cooling to assist in heat dissipation.
Some parallel optical communications modules have one or more heat sink blocks that are used in combination with an external heat dissipation device to perform heat dissipation. Lower surfaces of the heat sink blocks are mechanically and thermally coupled with the module circuit board. Upper surfaces of the heat sink blocks are exposed for mechanically and thermally coupling the blocks with the external heat dissipation device. Heat generated by the electrical and optoelectronic components of the module passes through the heat sink blocks and into the external heat dissipation device.
The upper surfaces of the heat sink blocks are generally planar surfaces that have small surface variations in them due to imperfections in the material (often copper) and/or manufacturing process used to make them. Compliant thermal pads are typically placed on the upper surfaces of the blocks and sandwiched in between the upper surfaces of the blocks and the lower surface of the external heat dissipation device. Because the thermal pads are compliant, or deformable, they conform to these surfaces. The compliant thermal pads fill in any surface variations to ensure that the thermal pathways between the heat sink blocks and the external heat dissipation device are uninterrupted.
The force that is needed for good electrical connectivity between the electrical contacts disposed on the lower surface of the module PCB and the electrical contacts disposed on the upper surface of the LGA socket may be, for example, 50 pounds (lbs). This force, referred to hereinafter as the electrical interconnectivity force, can cause the system PCB to deflect out of range of the LGA socket. A backing plate, sometimes referred to as a bolster plate, is sometimes used to prevent the system PCB from deflecting out of range of the LGA socket. The thermal pads are either designed to have inherent spring forces or are seated on springs to partially counter the electrical interconnectivity force to provide a proper thermal coupling force.
In order to create higher bandwidth optical communications systems, arrays of parallel optical communications modules are sometimes used with arrays of LGA sockets mounted on a system PCB. In such systems, it is more difficult to maintain the planarity of the system PCB, which makes it difficult to maintain the electrical interconnections between the modules and the respective LGA sockets. In such systems, it is even more difficult to prevent the electrical interconnectivity forces from causing the system PCB to be deflected out of range of the LGA sockets. It is also difficult in such systems to provide strain relief for the optical fiber cables associated with each of the modules and to prevent forces on the cables from being transferred to the modules, thereby adversely affecting the electrical interconnectivity between the modules and the respective LGA sockets.
A need exists for a heat dissipation system for use in an optical communications module that provides precisely-controlled electrical interconnectivity forces while also providing an effective heat dissipation solution. A need also exists for a way to provide strain relief for the optical fiber cables so that the interconnectivity between the modules and the sockets is not adversely affected by forces exerted on the cables.